Process for vacuum degasification of metal



Dec. 28, 1965 A. slcKBERT PROCESS FOR VACUUM DEGASIFICATION OF METAL 3Sheets-Sheet l INVENTOR /I//ff/ Filed May 29, 1962 ADOLF SIC/(BERT @wwwDufw mais Dec. 28, 1965 A. slcKBERT 3,226,224

PROCESS FOR VACUUM DEGASIFICATION OF METAL Filed May 29, 1962 3Sheets-Sheet 2 INV ENTOR ADOLF S/C/(BERT l f f f ,V /f fw uf//f f/ Dec.28, 1965 A. slcKBr-:RT

PROCESS FOR VACUUM DEGASIFIGATION OF METAL 3 Sheets-Sheet 3 Filed May29, 1962 INVENTOR ADOLF S/C/CEERT United States Patent O 3,226,224PROCESS FOR VACUUM DEGASIFICATION F METAL Adolf Sickbert,Wattenscheid-Eppendorf, Germany, as-

signor to Bochumer Verein fr Gusstahlfabrikation AAG., Bochum, Germany,a corporation of Germany Filed May 29, 1962, Ser. No. 200,599 Claimspriority, application Germany, .lune 9, 1961, B 62,840 7 Claims. (Cl.75-49) This is a continuation-in-part of co-pending applications SerialNo. 152,372, led September 27, 1961 (now U.S. Patent No. 3,146,503,granted September l, 1964), and Serial No. 153,842, filed November 21,1961, and now abandoned.

This invention relates to new and useful improvements in the vacuumdegasifcation of metal. In order to remove undesirable gas constituentsfrom various metals, including iron and steel, it is known to subjectthe metal to low pressures, as for example in vacuum chambers so thatthe partial pressures of the undesirable constituents will cause theirmigration out of the molten metal.

In accordance with one process for the vacuum degasification of metalwhich is particularly applicable for iron and steel but which is alsoutilizable in connection with other metals, the molten metal to bedegased is caused to liow into a vacuum chamber in the form of a sprayof droplets, Due to this particular form the action of the low pressurehas been found to be optimum in removing the undesirable gasconstituents. By `gas constituents is not only meant materials which arenormally considered as gases, but also other impurities which may beconverted to gas or vapor form under the pressures and temperatures inquestion. The above mentioned mode of vacuum degasication is sometimesreferred to in the art as stream degasication in that the major portionof the degasication occurs while the metal is flowing in the form of astream.

Stream degasiiication was conventionally effected by tapping the moltenmetal from the furnace or converter (generically referred to as furnaceherein) into a transport or storage ladle which may be of the tappingvariety, and thereafter transferring the molten metal from thisintermediate ladle into the vacuum chamber generally by means of afurther intermediate tapping ladle positioned directly above the vacuumchamber and hermetically sealed thereto. The use of the variousintermediate ladies however, resulted in a great loss of heat due to thehigh sensible heat content of the molten metal, and in order that themolten metal would remain sufficiently uid in the vacuum chamber andretain sufficient heat quantity for further handling and treatment itwas necessary to superheat the metal prior to leaving the furnace or toprovide additional heat during the intermediate handling, as forexample, by electrically heating one or more of the intermediate ladles.

Aside from the obvious expense involved in providing this additionalheat either by way of super-heating or through the intermediate ladles,the use of the higher temperatures required would adversely affect theequipment, as for example, the refractory linings thereof.

While it has been proposed in the literature of the art to effect adegasing of steel which has not been completely killed, the same was notsatisfactory from a commercial or practical standpoint due to thetendency of unkilled steel to violently boil in a transport ladle andthe danger which would inherently result therefrom.

In spite of the obvious disadvantages of the use of the intermediatetransport or storage ladles or containers, and the obvious economicaldisadvantages thereof, their use was universally believed necessary inthe art and no satisfactory solution had been proposed to avoid thesame.

One object of this invention is an improved mode of effecting the aboveidcntied stream degasing process without these disadvantages.

A further object of this invention is a greatly improved and moreefcient mode of effecting stream degasing of metal, such as iron andsteel. This and still further objects will become apparent from thefollowing description read in conjunction with the drawings in which:

FIG. 1 is a diagrammatic vertical section of an embodiment of equipmentfor effecting the process in accordance with the invention,

FIG. 2 is a diagrammatic vertical section of a further embodiment ofequipment for effecting the process in accordance with the invention,and

FIG. 3 is a vertical section of a still further embodiment of equipmentin accordance with the invention.

In accordance with the invention it has been suprisingly discovered thatstream degasing may be effected in a more efficient, economical andimproved manner if the molten metal is passed from the furnace in theform of a contiguous stream directly into the vacuum chamber wherein thedegasing occurs.

In accordance with the process of the invention the metal to be degasedis initially melted in the conventional manner in a furnace. The termfurnace is being generically used herein to designate any of the devicescon ventionally used for melting metal, as for example, open hearthfurnaces, electrical furnaces or converters in the steel art, or blastor shaft furnaces in the iron-making art. The molten metal formed in thefurnace after the melting and treatment therein is then directly passedin the form of a substantially contiguous stream from the furnacethrough an inlet opening into a vacuum chamber maintained at lowpressure while a pool of molten metal from said stream is maintainedabove the opening in the vacuum chamber in order to seal the same. Asthe stream of molten metal passes through the inlet opening which may bein the form of a nozzle into the vacuum chamber, the same is dividedinto a spray of droplets in accordance with the stream degasicationprocess. The `body of liquid metal which forms from the stream in thevacuum chamber is furthermore, if necessary or desired, subjected to theaction of the vacuum for further degasication.

The process in accordance with the invention is applicable for thedegasing of any metals, as for example, aluminum or other non-ferrousmetals, but is particularly adaptable for the degasiflcation of ferrousmetals, such as iron and steel, and partially ferrous metals such asferrochrome.

The invention will be described herein with further reference to thedegasiiication of steel, it being understood however, that the generalprinciples as described are also applicable to other metals. Inconnection with the degasiication of killed steel the pressure in thevacuum chamber should be maintained below about 20 mrn. Hg, whereas inconnection with unkilled steel the pressure should be maintained belowabout 30 mm. Hg. In connection with other metals pressures even as highas 50 or mm. Hg may be effective.

Referring to FIG. 1 of the drawing, 1 represents a tapping ladleconstructed from materials conventionally used for this purposes in thesteel-making art including, for example, a refractory lining. The ladle1 is provided with a vacuum-tight cover 2 which is provided with aconnecting tubular elbow 3 joined to the suction of evacuation pipe 4and provided with the closure valve 6. The suction pipe 4 and ifdesirable, the elbow 3, may be made of flexible material, or may beconstructed in a flexible manner by providing the ball and socket joints15. The suction pipe 4 is preferably also provided with cooling means inthe form of the pipes 17 surrounding the same and provided with thesprays or jets 19 through which a cooling agent such as compressed airis blown. The pipes 17 are also provided with the flexible links 20 sothat the same follow the movement of the suction pipe 4. Positioned onthe cover 2 is a relatively small feed hopper 5 which is funnel-shapedand may, if desired be provided with a stopper rod 13 constructed in themanner conventional for Stoppers in tapping ladles. The feed hopper 5 isheremtically sealed i.e. sealed in a vacuum-tight manner by thecylindrical sleeve 23 which surrounds the opening 7 leading through thecover of the chamber. The opening of the feed hopper 5 leading into theopening 7 may, if desired, be sealed by a removable sealing device suchas the plug 9. Surrounding the opening 7 is the splash shield or sleeve7a which protects the stopper device 8 of the ladle 1 from damage fromthe melted steel introduced. Additionally a feeding device for additivesr treating agents in the form of a lock-sluice or feed-worm 11 isprovided through which, for example, alloying deoxidizing agents orother treating agents may be fed. A television camera 12 may also beprovided to permit observation and control of the degasing operation.The entire arrangement as above described is moveable, as for example,on a conventional crane and hanger which engages the trunnions 4 so thatthe arrangement may be positioned directly below the discharge chute andtap 16a of a furnace such as the electric arc furnace 16. Due to themobility of the arrangement and the flexible connection of the suctionpipe 4 it is possible for the apparatus to follow the movements of thetapping chute 16a of the furnace. An overflow chute 14 for slag or thelike from the hopper is also provided.

In operation the steel is melted in the electric arc furnace, as forexample from scrap and pig iron, in the conventional manner, at atemperature between about 1600 and 1650 C. After the melt is formed, thesame may be killed in the conventional manner by adding treatingtreating agents, such as silicon, aluminum and calciumsilicon, whichwill combine with the oxygen in the molten metal, removing the same andforming a slag. The tapping ladle 1 in the form of the vacuum chamber isthen positioned by a crane beneath the tapping spout 16a of the furnace.If the stopper rod 13 is provided, the same is closed, and the ladle 1may be evacuated through the suction pipe 14, with the valve 6 open,down to the low pressure desired, as for example down to 0.5 milliameterHg or below, depending on the efliciency of the pump or evacuatingdevice. The furnace 16 is then tapped in the conventional manner throughthe tapping chute 16a, so that a stream of steel from the tapping chuteflows into the hopper 5. When the level of the steel in the hopper 5 issufciently high to seal the opening 7, the stopper rod 13 is lifted, sothat the steel will ow through the 4opening 7 into the interior of theladle 1. The pressure ,in the interior of the ladle 1 is maintainedthrough continuous evacuation, at as loW as possible a value, which inconnection with killed steel may remain at the values given above, butin connection with unkilled steel, due to the volume of gas generated,the pressure may somewhat increase. If a plug 9 is not provided, thesteel simply runs through the opening '7, and as the same enters theinterior of the ladle 1, is converted into a stream of droplets, theindividual particle size of which may range from about as tine aspossible to up to about ten millimeters. In this form the steel is veryeffectively degased by the low pressure in the chamber. The pouring ratevfrom the tap 16 is so controlled that a sufficient pool of molten steelremains in the hopper 5, so that the opening 7 will remain sealed. Itshould be emphasized that basically this is the sole purpose ofretaining the pool of steel in the hopper 5, and in connection with theefciency of the process, it is desirable that the smallest quantity ofthe steel be retained in this form and that the hopper be constructed assmall as possible for this purpose. The hopper 5 should, of course, belarge enough so that variations in the tlow rate from the tap 16a willnot cause an overow and spillage. Generally, the pool of molten steelshould be maintained at a height sufficient to prevent the down-ilowingsteel from completely cavitating through the opening which would allowthe sucking in of the ambient atmosphere. For practical considerations aheight of about 10 inches of steel in the -pool is generally suicientfor this purpose.

The pouring rate and rate of entry of the stream into the vacuum chambershould be so controlled that the stream will continue to divide into aspray of droplets, and generally for this purpose the opening 7 shouldhave a diameter between about 1 and 4 inches, depending upon the size ofthe furnace and rate of pouring, etc. The optimum size hole and rate ofpouring, for a particular operation however, may be very easilyempirically determined, as for example by observing the process throughthe television camera 12.

lf the tapping is effected so that slag runs olf with the molten metal,the ow rate may be so controlled that the slag, or a portion thereof, iscontinuously overowed from the top of the hopper 5, as for example intothe overflow chute 14. In certain instances it may be desirable to allowthe slag vor a portion thereof to also flow into the vacuum chamber, toact on the steel or as a heat-seal therefor. Thus, for example, theflowing of the slag with the steel into the Vacuum chamber, will resultin an intimate contacting which may be effective for desulfurization ofthe steel. It is also possible at the end of the operation to allow alayer of the slag to build up in the hopper 5 to maintain the seal andprevent excessive loss of temperature, particularly if the body of steelforming in the ladle 1 is to be subjected to further treatment under theaction of the vacuum, as for example stirred or admixed with treatingagents, alloying materials or the like. During the pouring operation itis also possible to admix treating agents with the stream of steel, asfor example by pouring the same into the hopper 5 or adding the same tothe hopper 5 during the pouring operation. Thus, for example, separateslag of various oxides, such as calcium oxide, aluminum oxide, siliconoxide, calcium fluoride, may be added for desulfurization or alloyingelements, or ennobling agents may be added, the term treating agentbeing used herein to generically define any additive conventionallyused, whether the same serves for removal of a component or remains inthe steel itself.

After the desired quantity of steel has been tapped from the furnace 16through the tapping spout 16a into the chamber 1, the chamber may besealed by closing the stopper rod 13 and allowing a body of metal orslag to remain in the hopper. The steel in the chamber 1 may then befurther subjected to the action of the vacuum until the same becomesquiescent, or partially quiescent, and further treating agents may beadded, if desired, as for example through the vacuum-tight sluice orlock 11. lf it is not necessary to maintain the vacuum at the low level,the Valve 6 may simply be shut, so that the pressure in the chamber willsimply increase in proportion to the gas generated.

If desired `or necessary, during the evacuation the suction pipe 4 maybe cooled, as for example by means of passing compressed air through thepipe 17, which is sprayed from the jets 19 in the form lof the sprays 18against the pipe 4. This is particularly desirable when treatingunkilled steel where a large quantity of hot gases are generated andmust be withdrawn through the pipe 4. The body of treated molten steelin the bottom of the vacuum ladle 1 may then be removed and treated inany known or conventional manner. Withdrawal of the steel may beeffected by simply lifting the stopper rod 8, so that the liquid steelwill run through the tap hole, melt the fusible membrane 10, as forexample of lead or the like, which serves the purpose of preventing gasfrom being initially sucked into the chamber through the tapping hole.If the ladle is to be transported prior to the removal of the steel, thevalve 6 may be shut and the ladle disconnected from the flexible pipe14. Alternatively, if it is not necessary to maintain the steel underlow pressure, the valve 6 may remain open. The steel from the ladle 1may, for example, be passed directly into a mold for casting an ingot orfoundry form, may be passed into a further vacuum chamber for furthervacuum treatment, and if desired cast in this chamber, under vacuum, ormay be subjected to continuous casting, directly or by way ofintermediate further vacuum treatment.

It should be emphasized that the stopper 13 does not function during thenormal operation and is merely utilized before and/ or after the pouringoperation. Within the broadest aspects of the invention it is notnecessary to provide such a stopper. If stopper 13 is not provided andthe apparatus is not sealed with plug 19, operation may still beeffected provided that the vacuum pump is of suticient high capacity sothat as the pouring ybegins and the sealing pool of molten steel buildsup in the hopper 5, evacuation of the chamber 1 may be effected in asufficiently short time. Alternatively, a plug 9, of fusible material,as for example lead, may be provided to allow initial evacuation of thechamber. When the pouring of steel is commenced and the sealing poolbuilds up in the hopper 5, the plug will automatically be melted away,allowing the steel to run into the chamber 1 as previously described. Itshould be furthermore emphasized that during the major portion of theoperation, the stream of steel from the furnace 16 into the chamber 1 iscontiguous, i.e., a continuous, uninterrupted stream of steel extendsfrom the furnace into the pool in the hopper 5 which continuously runsinto the chamber. Thus, in effect, it may be considered that the steelis poured directly from the furnace into the vacuum chamber, the pool ofsteel maintained above the vacuum chamber, merely serving the practicalfunction of sealing the inlet opening from the surrounding atmosphere.

In accordance with the invention it has been found that decidedadvantages may be achieved by directly pouring the unkilled steel fromthe furnace 16 into the chamber 1. The use of the unkilled steelenhances the degasification process and allows the killing of the steelin a more effective and efficient manner, with a reduced quantity, or insome cases without the special addition of a deoxidizing agent. Thus, asthe unkilled steel flows into the vacuum chamber, the carbon presenttherein will react with the oxygen in the steel, so that this carbonacts as a deoxidizing or killing agent, and the oxygen in turn acts as adecarbonizing agent, simultaneously reducing the oxygen and carboncontent. The reacted carbon and oxygen combine, forming gaseous carbonmonoxide, which is withdrawn with the gas. By a suitable initial oxygencontent in the steel or by the specific addition of oxygen, the carboncontent of the steel may be reduced to almost any desired value in avery simple and economical manner. This offers the possibility of verysimply producing extremely low carbon steel which is useful for manypurposes, as for example, producing sheets which are to be coated withvitreous enamel or as electrical laminates, such as for transformers.The carbon content thus, for example, may be reduced to 0.1% and lower.The formation of this low carbon steel furthermore allows the productionof a high silicon steel by the addition of silicon in further treatingoperations, which additionally adds to the heat economy of the processdue to its heat of dissolution.

The low carbon content steel which may be produced as described above isalso useful in the production of stainless steel, as for example, by theaddition of chromium.

Furthermore, the degasiiication of the unkilled or partially deoxidizedsteel allows a very accurate and convenient adjustment of the degree ofthe deoxidation through the vacuum and thus allows an accurate controlof the thickness of the non-segregated surface zone, as for example,when the steel is continuously cast from the vacuum chamber. Theinvention also allows the economical utilization of the evacuationequipment as it is possible to use a single evacuation pump or devicealternately or intermittently for various separate chambers. Thus forexample, the valve 6 may be shut and the suction pipe 4 connected to adifferent vacuum chamber after the pouring operation has terminated. Itis also often preferable to maintain the suction pipe 4 under the vacuumwhile it is being connected and disconnected to various devices in whichcase a separate valve may be provided in this line.

FIG. 2 shows a further embodiment of the invention in which aconventional tapping ladle 46 is positioned within the vacuum chamber 41provided with the hinged cover 2 connected to the main body of thechamber by means of the hinge 60. In this embodiment the hopper 47 is inthe form of a small cylindrical container provided with the tapping hole54 and positioned on the cover 2 in sealing engagement about the opening4S provided with the anti-splash shield 7a. The device as shown is usedin conjunction with the converter 52 and the molten steel from theconverter is poured through the guide chute 50 into the hopper 47. Thechute 50 being adjustable by means of the link 51. The vacuum tight sealof the hopper onto the cover 2 is effected by means of the sealing ring48. In all other respects operation is identical with the embodimentdescribed in connection with FIG. l, except after the pouring and vacuumtreatment the ladle 46 must be removed from the vacuum chamber byopening the cover 2.

In connection with tapping ladles, such as the tapping ladle 46, aproblem has been encountered in the prior art in that an accidentalunseating of the stopper rod would sometimes occur and result inspillage and loss of the molten steel from the ladle.

In accordance with a further embodiment of the invention as shown inFIG. 2, this is prevented by packing the tapping hole of the ladle withparticled refractory material such as the sand 52, and holding the sandin place by means of the plug 60 of wood, carbon refractory material orany other suitable material. The plug may be held in place by the hingedmetal plug 62 and spring latch 63. The accidental unseating of thestopper rod would simply cause the steel to flow in the sand andsolidify preventing accidental spillage and discharge. When it isdesired to discharge the steel through the tapping hole the latch 63 isreleased, the cover 62 to which the plug 60 may be attached swung out ofplace and the sand runs out of the hole allowing discharge in theconventional manner.

In the embodiment shown in FIG. 3 the device is used in conjunction withan open hearth furnace 64 provided with the discharge spout 65. In thiscase a conventional tapping ladle 46 is positioned in the vacuum chamber41 provided with the movable cover 2. The feed hopper 47 provided withthe opening 54 leading into the opening 66 in the cover 2 is sealed in avacuum-tight manner on the cover by means of the seal 67. An anti-splashdevice 7a is also provided. The tapping ladle 46 is however, sealed tothe bottom of the vacuum chamber 41 by means of the sealing ring 68 in avacuum-tight manner surrounding the discharge hole 69. This allowstapping of the ladle 46 without removal of the same from the vacuumchamber 41. If the stopper rod in the ladle 46 Will not provide ahermetic seal, or as a precautionary measure it is possible to seal thetap hole of the ladle 46 and/or the opening 69 with, for example, afusible plug or plate. In all other respects operation is as pre- "7viously described and the chamber 41 is evacuated through a conventionalhose connection (not shown).

The initial melting of the metal such as thesteel may as indicated, beeffected in the well known or conventional manner. In connection withthe melting of steel the melting operation prior to the tapping of thefurnace generally involves a refining and decarbonization treatment.Usually the initial charge for the furnace is made up with a highercarbon content than that ultimately desired in the steel to be formedand this carbon content is reduced during the decarbonization treatment.This decarbonization period generally takes about 1-2 hours, except inthe case of a blowing process. Where special quality or specialapplication steels are to be produced these rening and decarbonizationperiods often last for a considerably longer period of time. During thedecarbonization the carbon is converted to carbon monoxide by oxidationand the formed carbon monoxide causes an agitation of the melt andpromotes the purification, partial degasication and homogenization ofthe steel. The refining serves primarily to remove undesirablecomponents, especially non-metallics by reducing them with slags.

In accordance with a further embodiment of the invention it has beensurprisingly found that when utilizing the vacuum degasing treatment asdescribed above, the furnace may be initially charged with a chargehaving a carbon content not substantially in excess of that desired inthe ultimate steel to be produced and that the decarbonization treatmentmay be eliminated, thus substantially shortening the processing timewithout any detrimental effect on the quality of the steel. Inaccordance with this embodiment of the invention the `carbon content ofthe material when charged into the melting furnace, which is operated atatmospheric pressure, is kept within the range of the c-arbon contentrequired in the steel or blow. The charge is then melted down at thenormal melting temperature, as for example, at a temperature betweenabout 1500 and 1550 C., and after the charge is melted and without adecarbonization tre-atment the temperature is raised to the pouringtemperature, as for example between about 1600 and 1700 C. and thecharge is then immediately poured directly into the vacuum chamber forthe stream degasification, as described above. The reduction of meltingtime in this method may be about to more than 50% of the conventionalmelting time.

Prior to tapping the charge into the vacuum chamber, and preferablyprior to raising the temperature lto the pouring temperature, the meltshould be dephosphorized -if necessary, -as the lower temperature atthis point promotes dephosphorization. Furthermore, it is desirable tolower or oxidize out the silicon content, including any ferrosiliconthat may have been added. The slag is drawn off and a new slag -or newslag-forming agents may be added. Furthermore, any necessary correctionand alloy element contents may be made before tapping, or if desired,during tapping. Thus, for example, if the initial charge is selectedwith a carbon content below that desired in the steel, carbon preferablyin the form of graphite powder may be added at this point. While theheating of the charge may be effected in any of the known furnaces, thesame is preferably effected in an electric arc furnace as the sameallows a very rapid heating-up and thus a very substantial saving in theprocessing time. The vacuum stream degasing is effected in the mannerdescribed above and pressures below 30 mm. Hg, and preferably below 20mm. Hg are used with the upper limit being contemplated in connectionwith completely unkilled steel. For higher grades of steel it ispreferable to use pressures of less than 3 to 0.5 mm. Hg, and preferably0.11 mm. Hg. After tapping the steel may be treated and processed in theidentical manner as described above and the other expedients .describedare also applicable. The treatment in accordance with this preferredembodiment of the invention results in a substan-r tial saving in timein which the melt is heated in the furnace and thus in a substantialeconomy without any detrimental eifect on the steel quality whatsoever.

The invention will be described in further detail with reference to thefollowing examples which are given solely by way of illustration and notlimitation.

Example 1 A 50-ton charge consisting of 90% scrap and 10% pig iron wasmelted, by heating to a temperature of about 1500" C., in an electricarc furnace of the type shown in FIG. 1. The melt formed had acomposition of .40% C, .35% Mn, .06% Si, .035% P, and .032% S.

2000 lbs. of burnt lime, lbs. of CaF2 and 600 lbs. of iron ore aresuccessively added into -the furnace. The temperature of the melt isthen raised to about 1600 C. over a period of about 45 minutes. Duringthis period and after the additives had formed a liquid slag, normalcubic meters of oxygen were blown into the liquid melt. As a result `ofthis treatment the melt had a composition of .10% C, .25% Mn, .00% Si,.012% P and .032% S. The slag was partially removed and the melt whichcontained about 6 p.p.m. H2, 0.006% oxygen and about 0.005% nitrogen,was treated -by the addition of manganese to bring the content to .35%.

The steel was then tapped from the furnace into an apparatus as shown inFIG. 1 and having a 70ton capacity. The size of the opening 7 was 1%inches in diameter and the splash guard 7a had a length of 20 inches.The capacity of the hopper .5 was five tons. The ladle 1 was evacuatedthrough the suction pipe 4 to a vacuum of about 0.2 millimeter Hg,utilizing a vacuum pump. When the steel reached the level of about 12-14inches in the hopper l5, the stop rod 13 was raised and the fusible plug9 of lead melted, causing the steel to flow downward through the opening7 and into the chamber in the form of a spray of particles having a sizeof below about 10 millimeters. Due to the fact that the steel wasunkilled and relatively large quantities of gas generated, the pressurein the ladle 1 rose to about 2 millimeters Hg. The pipe 4 became heateddue to the hot gases drawn off and were cooled with lthe compressed airjets 13. The rate of pouring from the furnace 16 was maintained at about6 tons per minute, which maintained a substantially uniform height ofthe liquid pool in the hopper -5 at between about 10-20 inches. Afterthe complete charge had been emptied into the ladle 1, `the stopper 13was closed and the hopper 5 substantially filled `with the slag from thefurnace. The steel was maintained in the ladle 1 under the influence ofthe vacuum until it was substantially quiescent, which took about 6-10minutes.

The liquid steel charge contained in the ladle 1 was thus partiallykilled by the degasication action and the reaction of oxygen with thecarbon reducing the carbon content to .08%. The valve 6 was then closed,the suction pipe 4 disconnected, the valve 6 opened to allow entry ofthe ambient atmosphere. The ladle was then transported by a crane andthe steel tapped from the ladle by lifting the tapping rod 8. Thiscaused a melting of the fusible plate 10, and the stream of steel waspoured into an ingot mold for the formation of a plate ingot. The gascontent of the treated steel was reduced to 11/2 parts per millionhydrogen and .002% oxygen and .003% nitrogen.

Example 2 Example 1 was repeated except that 250 normal cubic meters ofoxygen were blown into the melt to reduce its carbon content to .03%.The steel obtained after the degasing operation as described in Example1 had a carbon content of .008% and was excellently suited forapplications requiring low carbon steel, as for example pro- 9 ducingplates for enameling, transformer laminates, and the like.

Example 3 Example l was repeated except that the steel was initiallykilled in the furnace by first removing the liquid oxidizing slag andadding 2% burnt lime, 1/2 CaF2, and 100 kg. ferro-silicon having a 75%silicon content. After these additives had formed a surface slag, 30 kg.of carbon powder were distributed over the surface of the slag. 175 kg.of ferro-silicon were then added to the melt and the killed meltobtained was tapped into the vacuum device as described in Example 1. Asthe stream passed into the vacuum device, 250 kg. of a desulfurizingslag containing calcium oxide, aluminum oxide, silicon dioxide, CaFZ andFeSi, were added over the period of the pouring through the sluice 11.This resulted in a reduction of the sulfur content to below .010%. Themelt in the ladle was then magnetically stirred unde the action of thevacuum for minutes and ingots were cast from the steel, as for examplefor the production of boiler plate steel.

Example 4 Example 1 may be exactly repeated except the steel produced ina converter, rather than the electric arc furnace.

Example 5 A 60-ton charge of 60% scrap and 40% pig iron was melted in anopen-hearth furnace to obtain an initial temperature of the melt ofabout l500 C. The melt contained 1% C, .35% Mn, .06% Si, .035% P and.032% S.

The steel was heated and treated in the conventional manner for about 2hours, resulting in a melt which contained .35% C, .30% Mn, .020% P and.022% S. The steel was then tapped into the vacuum ladle as described inExample l, and a treating agent in the form of .2% Mn was added to thestream of the steel as it flowed into the hopper 5. After the pouringhad been completed .25% silicon, in the form of ferro-silicon, was addedthrough the sluice 11 and the melt magnetically stirred for 5 minuteswhile the melt was maintained under vacuum.

The magnetic stirring is effected by constructing the ladle with itsbottom portion to the height of about 1 meter of non-magnetic steel andsurrounding this bottom with a rotating magnetic field provided througha coil. The ladle was then disconnected from the suction line andtransported and sealed in place on the top of a second vacuum chamberprovided with a forging mold. The steel was then tapped from the ladle 1into the second vacuum chamber directly into the forging mold. Thesecond vacuum chamber was maintained under a pressure at least as low asthe pressure in the first vacuum chamber during the initialdegasification. As molten metal poured from the ladle 1 into the secondvacuum chamber, it was subjected to a second stream degasication. In thesame manner, instead of being directed into the second vacuum chamber,the steel may be continuously cast as it leaves the ladle 1.

Furthermore the molten steel may be directly tapped from the ladle 1into a foundry mold.

Example 6 In a 50-ton electric arc furnace with a transformer output of20,000 kw., the following material was charged:

Kg. Scrap 48,000 Pig iron 2,000 Calcined lime 1,200 Iron ore 800 Withthis charge the following analysis was theoretically expected when themeltdown became complete:

Percent C 0.45 Mn 0.55

Cr, Ni, and Cu were expected to be present only in slight amounts astolerable impurities.

The first test should produce the following approximate analysis in viewof the changes known by experience to occur during the melt-down:

Percent C 0.35 Si Less than 0.02 P 0.018 S 0.031

The standard analysis for CK 35 carbon steel for crankshafts is asfollows:

C 0.32 to 0.37. Mn 0.50 to 0.70. Si 0.15 to 0.35. P 0.020 max. S 0.015max.

The scrap was fully melted down after 2 hours. In the last 20 minutesbefore sampling, 250 kg. of lump ore and 50 kg. fluorspar were shoveledby hand into the slag, and then the melt was tested.

Test 1 gave the following analysis:

Percent C 0.30 Nin 0.41 S1 0.01 P 0.017 S 0.033 Cr 0.04 N1 0.07 Cu 0.11

Therefore, the addition of lime and ore to the charge and the laterinjection of a small amount of ore resulted in a dephosphorizationduring the melt-down to 0.017% P, while the theoretically expectedcontent was 0.031%.

In the case of sulfur, the corresponding figures were 0.042% S and0.033% S in the sample.

The first slag was largely drawn off and a new slag was added having thefollowing composition:

Kg. Ground Calcined lime 1,400 Fluorspar (ground) 450 Coal dust 50Silicon dust The sample of the melt had a temperature of 1530" C. Thenthe heat input was increased with a higher power output. In 45 minutes atemperature of l670 C. was reached. In the meantime, an electricagitator was run several times for several minutes each time to stir upthe steel bath and the slag.

20 minutes before tapping 110 kg. FeMn (75% Mn) were thrown into thefurnace to bring the manganese content up to within the prescribedlimits (0.50-0.70% Mn); the addition was calculated to make it 0.56% Mn.

During the heat-up period of 45 minutes provision was made by theaddition of 60 kg. silicon dust (75 and 32 kg. coal dust to produce areducing slag and to keep its reducing power constant or improve it.

minutes before tapping, Sample 2 was taken, which showed the followinganalysis:

C .Percent 0.34

Mn do 0.56

Si do 0.06

P do 0.018

S do 0.023

H2 6.1 cc./100 g. steel. O2 -Percent 0.007

N2 do 0.007

Shortly before tapping another sample was taken from the furnace (Sample3) and showed the following analysis:

C .Percent 0.33 Mn do 0.56 Si do 0.23 P do 0.017 S do 0.018 H2 6.4 cc.per 100 g. O2 .Percent 0.008 N2 do 0.007

Immediately after Sample 3 120 kg. FeSi (75% Si) were thrown into thefurnace to bring the silicon content of the heat up to about 0.30%according to the standard.

2 hours and 45 minutes after the current was turned on, the charge wastapped and at the same time subjected to a vacuum treatment in adegasing ladle as shown in FIG. 1. The pressure in the vacuum equipmentwas 0.1 mm. Hg at the beginning and did not exceed 2.0 mm. Hg during thetreatment.

After tapping the fourth sample analysis was as follows:

C Percent 0.36 Mn do 0.58 Si do 0.27 P do 0.018 S do 0.014 H2 1.2cc./100 g. O2 .Percent 0.003 N2 do 0.005

The tapping temperature was 1680o C. and the pouring r temperature 1570C. The current consumption amounted to 578 kwh. per metric ton for amelting time from tap to tap of 3 hours 10 minutes, whereas the meltingtime in this furnace under the operation methods used hitherto wouldhave amounted to about 5 to 51/2 hours.

5ton ingots were top-poured with hot tops. The pouring rate was about21/2 metric-tons per minute. The steel corresponded at least to steelmade in the normal manner, in all its chemical and physicalcharacteristics namely in cross samples from top and bottom, Baumannprint, etch test, blue shortness tests, purity in core and skin,analyses of skin and core for C, S, O and N, in specimens from thecenter of the ingot, longitudinal tear specimen from skin and core asdelivered and after cooking out at about 160 C. notch impact strengthtransition temperature in skin and core on longitudinal specimens,microstructure in skin and core, fracture structure in skin and core,hydrogen analysis from the core, conversion behaviour, annealingcharacteristic, Baumann print (transverse), etch test (transverse), blueshortness, purity in skin and core, analysis for C, S, O and N from skinand core.

Example 7 A steel was to be made for dies with the following specifiedanalysis:

Percent C 0.53-0.58 Si O20-0.35 Mn 0.50-0.70 P 0.020 S 0.020 Cr 0.60-080 Mo 0.30-0 35 Ni 1.50-1.80 Va 0.07-0.12

The charge melted down in the arc furnace showed the following analysison the first test:

Percent C 0.45 Si 0.12 Mn 0.55 P 0.025 S 0.016 Cr 0.73 Mo 0.33 Ni 1.70Va 0 The silicon content has been lowered extensively by the addition ofore. The melting down temperature amounted to 1510 C. 15 minutes afterthe first test the melt was slagged off and a light carbidic slag wasadded. Shortly before the expiration of an hours heat-up timeferrovanadium, ferromolybdenum and some aluminum were added to the melt.After an hour the temperature reached 1695 C. and the melt was directlypoured into the tapping ladle shown in FIG. 1 at a temperature of about1690 C. During the entire tapping time the pressure in the Vacuum ladlewas less than 5 torr. The duration of this vacuum treatment was about 7minutes. The charge was poured from the tap ladle into an ingot moldthat had been set up in a vacuum chamber. The vacuum there was about 1torr. The pouring of the 10- ton ingot took about 10 minutes. 0.10%graphite was added to correct the carbon content. The steel of thisingot gave the following final analysis:

Percent C 0.57 Si 0.21 Mn 0.59 P 0.015 S 0.007 Cr f 0.77 Mo 0.35 Ni 1.57Va 0.10 A1 0.01

This steel had strength qualities entirely in accordance with thosefound in steels of this type when they are made by the former methods.

While the invention has been described in detail with reference tocertain specic embodiments, Various changes and modifications which fallwithin the spirit of the invention and scope of the appended claims willbecome apparent to the skilled artisan. The invention is therefore onlyintended to be limited by the appended claims or their equivalents,wherein I have endeavored to claim all inherent novelty.

What I claim is:

1. Process for the vacuum degassing of metal which comprises melting themetal in a furnace under substantially atmospheric pressure; directlypassing a contiguous stream of the molten meltal downwardly from thefurnace into a container open to the atmosphere and surrounding theinlet opening of a vacuum chamber maintained at an absolute pressurebelow mm, Hg and through said inlet opening into the vacuum chamber,maintaining the flow rates of molten metal from the furnace to thecontainer, and through the inlet opening into the vacuum chamber inrelation to each other to maintain a pool of molten metal with an uppersurface open to the atmosphere in said container to seal the inletopening, thereby preventing loss of vacuum in the chamber; separatingslag entrained in the molten metal from the surface from said moltenmetal in the container by flotation upward to said surface open to theatmosphere, passing a molten metal stream through said inlet opening,dividing said stream into a spray of droplets as it passes into thevacuum chamber; and removing said separated slag from the surface of themolten metal pool so that the metal introduced into the vacuum chamberis substantially slag-free.

2. Process according to claim 1 in which the metal is steel.

3. Process according to claim 1 in which said metal is a ferrous metaland wherein the pressure in the vacuum chamber is maintained below 50mm. Hg.

4. Process according to claim 3 in which said metal is steel and whereinthe pressure in the vacuum chamber is maintained below 30 mm. Hg.

5. Process according to claim 4 in which the stream of molten steel ispassed from the furnace in a substantially unkilled condition and is atleast partially killed as it passes into the vacuum chamber.

6. Process according to claim 1 in which said metal is steel which ismelted in the furnace from a charge having carbon content approximatelyequal to the carbon content of the steel to be produced and in which thetemperature of the melt is raised to the pouring temperature immediatelyprior to passing said stream into the container.

7. Process according to claim 6 which includes dephosphorizing the meltprior to raising the temperature thereof to the pouring temperature.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCESAIMME Transactions (Iron and Steel Division), published by theInstitute, New York, 1929, pp. 428-445, article by Ziegler,

Metals and Alloys, vol. 1, No. 15, September 1930, pp. 712-713.

The Making, Shaping and Treating of Steel, 7th ed., 1957, United StatesSteel Corp., Pittsburgh, Pa., p. 314.

Transactions of the American Electrochemical Society, vol. 32, 1917, pp.165-182, articles by Yensen.

DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

1. PROCESS FOR THE VACUUM DEGASSING OF METAL WHICH COMPRISES MELTING THEMETAL IN A FURNACE UNDER SUBSTANTIALLY ATMOSPHERIC PRESSURE: DIRECTLYPASSING A CONTIGUOUS STREAM OF THE MOLTEN METAL DOWNWARDLY FROM THEFURNACE INTO A CONTAINER OPEN TO THE ATMOSPHERE AND SURROUNDING THEINLET OPEING OF A VACUUM CHAMBER MAINTAINED AT AN ABSOLUTE PRESSUREBELOW 100 MM. GH AND THROUGH SAID INLET OPENING INTO THE VACUUM CHAMBER,MAINTAINING THE FLOW RATE OF MOLTEN METAL FROM THE FURNACE TO THECONTAINER, AND THROUGH THE INLET OPENING INTO THE VACUUM CHAMBER INRELATION TO EACH OTHER TO MAINTAIN A POOL OF MOLTEN METAL WITH AN UPPERSURFACE OPEN TO THE ATMOSPHERE IN SAID CONTAINER TO SEAL THE INLETOPENING, THEREBY PREVENTING LOSS OF VACUUM IN THE CHAMBER; SEPARATINGSLAG ENTRAINED IN THE MOLTEN METAL FROM THE SURFACE FROM SAID MOLTENMETAL IN THE CONTAINER BY FLOTATION UPWARD TO SAID SURFACE OPEN TO THEATMOSPHERE, PASSING A MOLTEN METAL STREAM THROUGH SAID INLET OPENING,DIVIDING SAIS STREAM INTO A SPRAY OF FROPLETS AS IT PASSES INTO THEVACUUM CHAMBER; AND REMOVING SAID SEPARATED SLAG FROM THE SURFACE OF THEMOLTEN METAL POOL SO THAT THE METAL INTRODUCED INTO THE VACUUM CHAMBERIS SUBSTANTIALLY SLAG-FREE.